Store Lua class object to C pointer and push it back to Lua Stack

Question

Using a home made Lua C++ binding I'm able to create C++ classes that are available from Lua scripts.

Now I would like to create class objects in a Lua script, store its reference in C++ and when required call a function of this Lua class object from the C++ code.

In a Lua script I created a class object with a global function to pass it to the C++ code.

MyClass = {}

function MyClass:hello()
    debug.codeSite.sendMsg( "MyClass:hello()" )
end

function MyClass:new()
  local tNewClass = {}

  setmetatable( tNewClass, self )
  self.__index = self

  return tNewClass
end

local tClass = MyClass:new()

function getClass()
    debug.codeSite.sendMsg( "Return class object" )
    return tClass;
end

Now in C++ I would like to get its instance and call the function hello(). Here what I tried :

Call getClass() so it pushes the Lua object (a table) to the stack.
Store its address into a C++ const void* using function lua_topointer().

At this point I don't know how to push back this pointer to the Lua stack, so the Lua table is pushed back to the stack, push the function name and then call it.

The idea of all of this is to create several objects in Lua scripts and use them in C++.

In lua:

tObject1 = MyClass:new()
tObject2 = MyClass:new()

and in C++ use tObject1:hello() or tObject2:hello() when required.

Edit:

According to this description of lua_topointer(), converting Lua table to C pointer is only for debugging purpose.

Thanks.

Vlad Vlad · Accepted Answer · 2016-03-18T15:45:50

Store lua objects in predefined Lua registry table with luaL_ref(), and save returned integer index in c++. When you need Lua object put on Lua stack, read it from registry with lua_rawgeti(), using index retrieved earlier. Don't forget to unref object with luaL_unref() when you don't need it on c++ side anymore.

Store Lua class object to C pointer and push it back to Lua Stack

1 Answers